The subject matter disclosed herein relates generally to magnetic resonance imaging (MRI) systems, and more particularly to systems and methods for reducing preamplifier oscillation in MRI systems.
Magnetic Resonance Imaging (MRI) systems include a magnet, such as a superconducting magnet that generates a temporally constant (i.e., uniform and static) primary or main magnetic field. MRI data acquisition is accomplished by exciting magnetic moments within the primary magnetic field using magnetic gradient coils. For example, in order to image a region of interest, the magnetic gradient coils are energized to impose a magnetic gradient to the primary magnetic field. Transmit radio-frequency (RF) coils are then pulsed to create RF magnetic field pulses in a bore of an MRI scanner to selectively excite a volume corresponding to the region of interest in order to acquire MR images of the region of interest using receive RF coils. During the transmission of the RF magnetic field pulses, the receive RF coils are decoupled or disabled and during reception the transmit RF coils are decoupled or disabled. The resultant image that is generated shows the structure and function of the region of interest.
Preamplifiers in MRI systems, which are used to amplify the received MR signals, are increasingly placed closer to the imaging coils, such as on-coil preamplifiers. These on-coil preamplifiers increase the preamplifier-decoupling performance in multi-channel coil arrays, which results in an improved signal to noise ratio (SNR) and improved acceleration performance. However, placing the preamplifiers in the vicinity of the coil elements opens a new feedback path that can easily cause oscillation, resulting in degraded imaging performance of the MRI system.
Conventional systems attempt to reduce the preamplifier feedback using devices to reduce the feedback from the preamplifier into the coil array, such as input baluns, output baluns, additional shielding, additional isolation, etc. These devices can add cost and complexity to the system. Additionally, preamplifier-decoupling performance is adversely affected, for example, as a result of increased preamplifier input impedance from input baluns.